The present invention relates to a drum driving device for a window shade and, more particularly, to a drum driving device for a window shade that is simple in structure and reliable in operation.
A drum driving device disclosed in China Utility Model No. 200820044961.2 includes a single direction clutch device mounted between a drum and a cord pulley. The clutch device is comprised of a shaft coaxially mounted to the drum for driving the drum to rotate and a slideable rotary seat coaxial to the shaft for clutching purposes. An end face of the shaft coupled to the rotary seat includes teeth for single-direction coupling. A housing includes an axial hole coaxial to the drum. The shaft has a clutch shaft section to which an end of the rotary seat is engaged. The engaging location of the clutch shaft section and the end of the rotary seat is in the axial hole. The other end of the rotary seat is located in a socket in a side of the cord pulley and includes an inclined groove receiving a sliding block formed in the socket. In operation, when the cord pulley is rotated by pulling a pull cord, the sliding block slides along the inclined groove to push the rotary seat towards the shaft, causing engagement between the end of the rotary seat and the end face of the shaft. The shaft is rotated by the rotary seat to drive the drum to rotate. When the pull cord is released, the cord pulley rotates in a reverse direction under the action of a return spring to wind the pull cord around the cord pulley. At the same time, the slide rotates in the reverse direction together with the rotary seat and moves along the inclined groove away from the shaft to disengage the rotary seat from the shaft while under the action of a compression spring. Thus, the shaft rotates freely, allowing joint, smooth rotation of the shaft and the drum. However, friction exists between the sliding block and the inclined groove. Frequent use causes wear to the sliding block and the inclined groove. In particular, when the sliding block stops in a location in the inclined groove and then starts to move, the pressure imparted to the sliding block is relatively large. Furthermore, the static friction is larger than the sliding friction. Thus, the inclined groove is liable to wear, causing non-smooth movement of the sliding block and causing malfunction of the clutch device. Further, the clutch device is complicated and, thus, has high manufacturing costs.
Thus, a need exits for a drum driving device for a window shade that is simple in structure and reliable in operation.